Geometry Effects on Detonation Performance in Ideal and Non-Ideal High Explosives

Mark Short, P.h.D.

A detonation is a complex, compressible flow-reaction driven structure consisting of a lead shock wave and subsequent reaction zone in which reactants are converted into products. In high explosives, the primary purpose of detonation is to do work on surrounding inert materials, such as rock in mining applications. This requires the ability to model the speed and path of a detonation as it moves through often complex three-dimensional geometries with various confinements, as well as the subsequent energy release due to reaction which drives surrounding materials. The high pressure of detonation products results in yielding of any confinement at the explosive edges, and the reaction zone structure of a detonation, which controls the propagation dynamics and energy release, becomes multi-dimensional and determined by a complex interaction between streamline divergence, compressibility and reaction.

The scale disparity between a typical reaction zone thickness and larger explosive geometry can be of the order of several hundred or thousand, and thus for many applications detonation performance is modeled by a class of models known as programmed burn. These models separate the detonation performance calculation into two components: the detonation motion, described by a surface evolution description, and an energy release component, in which reaction is initiated by the surface wave calculation. In this talk, I will describe a combined experimental and theoretical study conducted with Scott Jackson (Los Alamos) on the effects of geometry and material confinement variations on an advanced programmed-burn timing model for detonation propagation known as Detonation Shock Dynamics (DSD). In the DSD model, the normal speed of the detonation timing surface-wave evolution is related to the local curvature of the surface. Typically the calibration of the DSD model for a given high explosive is conducted in a single geometry such as a cylindrical rate-stick of explosive, and then applied to arbitrarily complex geometries. Here we will examine the predictive capability of this approach comparing results of experiments conducted in 2D axisymmetric cylindrical and planar geometries for three classes of explosives, namely ideal (PBX 9501), insensitive (PBX 9502) and non-ideal (ANFO). We will also discuss an asymptotic study of the DSD model for understanding the effects of geometry and confinement changes on the detonation motion. We will begin the talk with a basic description of the fundamentals of detonation wave propagation physics.